1. Field of Art
The present disclosure relates to optical scanning devices that scan surfaces to be scanned with a plurality of beams, to methods for manufacturing such optical scanning devices, and to image forming apparatuses.
2. Description of the Related Art
In recent years, there has been an increasing demand for image forming apparatuses, such as a laser beam printer and a digital copier, to form high-resolution images at high speed. To meet such a demand, an image forming apparatus is typically provided with an optical scanning device that includes a light source, such as a semiconductor laser array, having a plurality of light emitters, and the optical scanning device scans a surface to be scanned (i.e., photosensitive drum surface) simultaneously at a plurality of locations aligned in a sub-scanning direction.
In such an optical scanning device, a plurality of light beams incident on the photosensitive drum surface may be specularly reflected and, as a result, may return to the plurality of light emitters, leading to a problem that the plurality of light emitters oscillate unstably. In addition, the specularly reflected light beams may be reflected by a surface of an imaging optical system provided in the optical scanning device, and the reflected light beams may again become incident on the drum surface, leading to a problem that a ghost image appears. To solve these problems, in an existing technique, a plurality of light beams are made to be incident on a photosensitive drum surface so as to be oblique to a normal of the photosensitive drum surface, as illustrated in FIG. 8.
The photosensitive drum surface, however, is curved in a sub-scanning section, and thus a configuration such as the one illustrated in FIG. 8 may increase mutual differences in scanning magnification among a plurality of scanning lines on the photosensitive drum surface. Consequently, as illustrated in FIG. 8, a deviation D may be generated, in a main scanning direction, between imaging positions on the photosensitive drum surface, which may produce a difference between drawing start positions of scanning lines, and thus a high-quality image may not be obtained. Hereinafter, such an imaging position deviation in the main scanning direction will be referred to as a “drum oblique incidence jitter.”
U.S. Pat. No. 6,256,132 discloses an optical scanning device configured to cancel an imaging position deviation in a main scanning direction resulting from a light beam incident on an imaging lens being a convergent light beam, and a drum oblique incidence jitter. In addition, U.S. Pat. No. 6,459,520 discloses a method for correcting an imaging position deviation in a main scanning direction by electrically controlling light emission timings of a plurality of light emitters.
In the optical scanning device described in U.S. Pat. No. 6,256,132, however, the drum oblique incidence jitter is corrected on the basis of an assumption that the optical scanning device is constructed in accordance with certain design values, and thus individual differences in the drum oblique incidence jitter caused by optical and mechanical arrangement errors of each component are not taken into consideration. Therefore, the optical scanning device described in U.S. Pat. No. 6,256,132 is unable to correct the drum oblique incidence jitter accurately because individual differences are not taken into consideration. Furthermore, U.S. Pat. No. 6,459,520 merely discloses a method for correcting an imaging position deviation in the main scanning direction and does not disclose a method for correcting the drum oblique incidence jitter.